The aim of my thesis is to explore the macroeconomic impacts of the projected demographic changes in Greece. Population of Greece is projected to age in the course of the next three decades. The thesis combines demographic projections with a multi-period economic Computable General Equilibrium (CGE) modelling framework to assess the macroeconomic impact of these future demographic trends. The size and age composition of the population in the future depends on current and future values of demographic parameters such as the fertility, mortality rates and the level of annual net migration. I use FIV-FIV demographic software in order to project population changes for 30 years. Total population and working age population changes are introduced as exogenous disturbances to the G-AMOS CGE modelling framework calibrated for the Greek economy for the year 2004. The economic impacts of a very wide range of demographic scenarios are examined. The main finding is that positive net migration is able to cancel the negative impacts of an ageing population that would otherwise occur as a result of the shrinking of the labour force. The very serious policy implication is that a viable, long-lasting migration policy should be implemented, while the importance of policies that could increase fertility should also be considered.